An \(L^2\) -bounded integral operator \(T_K\in \mathbb {B}(L^2({\mathbb {R}}^n))\)  with a standard kernel \(K\)  is called a Calderón–Zygmund operator. Then we have the following theorem (see [1]} for the item (1) and [2]}, [3]} for the item (2), respectively):
